This invention relates to electronic component packages and in particular to packaging semiconductor chips which require a high density of external electrical connections.
At the present time, the standard method of assembling postmolded plastic integrated circuit packages begins with a lead frame. The lead frame may be visualized as a solid metal picture frame with slender fingers radiating inward from either two opposing sides or from all four sides toward the geometric center of the picture frame. Also radiating inward from each of the four corners of the picture frame is a slender finger which terminates on a square or rectangular piece of metal, typically referred to as a paddle, which occupies a portion of the area around the geometric center. The chip is first epoxied to the paddle and then electrically connected to the lead frame by wire bonds which originate at the contact pads on the chip and terminate on the fingers. It should be noted that the lead frame fingers stop short of contacting the paddle in order to electrically isolate the two entities. The chip and a portion of the lead frame fingers are then encapsulated, or molded, in a material such as an epoxy or plastic molding compound. Finally, the molded package body and lead frame fingers are excised from the metal picture frame portion of the lead frame. The lead frame fingers are then formed to provide a means of electrically connecting the integrated circuit package to the second level interconnection board (see, e.g., U.S. Pat. No. 4,048,670 issued to Eysermans).
The standard packaging scheme has been generally satisfactory. However, the increasing complexity of dsign and function of single chips, such as microprocessors, has required a higher density of chip contact pads and consequently, higher I/O connections for the packaged device. In order to meet the need for packages requiring a high contact pad density, workers in the art have generally relied upon multi-level ceramic or glass packages (see, e.g., U.S. Pat. No. 4,498,122 issued to Rainal). While adequate, such packages are fairly expensive.
It is therefore a major object of the invention to provide a small and inexpensive semiconductor chip package that can accommodate chips with a high contact pad density.